Hot melt liquid adhesives are used in a number of different applications throughout industry for adhering a material to an object or to another material. Such adhesives are generally dispensed by a gun apparatus through a nozzle onto the material. In some applications, it is sufficient to extrude a simple line or bead of adhesive on the material. However, in other particular applications, it is desirable to swirl or disturb the adhesive bead by engaging it with a flow of pressurized air from jets or other orifices, such that the air flow swirls or flings the adhesive around to create a wide adhesive pattern which comprises generally thin overlapped fibers or strands of adhesive.
Adhesive dispensing equipment for creating such spray patterns generally includes a dispensing gun apparatus and at least one gun nozzle which is coupled to a supply of liquid adhesive by an adhesive line and to a supply of pressurized air by an air line. In operation, hot melt adhesive flows through the adhesive line of the gun to the nozzle and is extruded from the nozzle as a bead of adhesive. Pressurized air is then directed from the end of the nozzle toward the bead of adhesive to disturb or move the adhesive bead or otherwise control how it is applied and sprayed on the surface of interest. A nozzle cap generally surrounding the nozzle has a particular shape and configuration which controls the air and its cooperation with the adhesive to achieve the desired spray pattern.
One way of applying a sprayed pattern of adhesive is to swirl the adhesive in controlled circles. In swirled adhesive spray patterns, the pressurized air directed toward the dispensed bead of adhesive is controlled to stretch or attenuate the bead into a thin fiber or strand and to precisely move the strand around in a generally circular pattern. The finished pattern of applied adhesive on the surface comprises numerous, overlapping circles of thin adhesive strands as opposed to a singular, thick bead of adhesive. One application for a swirl technique is the bonding of nonwoven fibrous material to a polyurethane substrate in articles such as disposable diapers, incontinence pads and other related articles. For example, U.S. Pat. Nos. 4,969,602; RE33481; 4,983,109; 5,026,450, 5,065,943, and 5,194,115 all owned by the assignee of the present application, disclose various apparatus and methods for applying hot melt thermoplastic adhesives in overlapping, circular swirls of adhesive.
In the automotive industry, solvent based adhesives have traditionally been used, for example, to join carpet to the interior portion of a door. However, in order to overcome some inherent limitations associated with such solvent based systems, the automotive industry is investigating other bonding systems, such as hot melt adhesives. Unfortunately, attempting to apply hot melt adhesives suitable for the automotive industry in a stable pattern is different than applying hot melt adhesives to diapers.
The typical adhesives utilized in automotive applications are generally thermo-setting, polyurethane adhesives which are particularly viscous, and therefore, have different spray properties than the various types of hot melt adhesives utilized in other adhesive dispensing applications, such as those used in the disposable diaper industry. Therefore, while the nozzles utilized to dispense hot melt adhesives for other industries may be adequately suited for those particular applications, they may not be particularly suited for applying thermo-setting polyurethane adhesives in a fibrous spray pattern for automotive applications.
Specifically, it has been found that spray patterns of viscous polyurethane adhesive generated through some existing nozzle and cap assemblies did not produce a suitable stable pattern. For example, the pattern of adhesive tended to shift during spraying, and the spray pattern did not remain consistent from day to day. Additionally, it was difficult and sometimes impossible to achieve a suitably wide adhesive pattern.
Furthermore, with at least one currently existing nozzle assembly, fibers of the sprayed adhesive material had a tendency to swing up from the spray pattern and hit the nozzle, sticking to the nozzle and blocking the flow of pressurized air utilized to control the spray pattern. Apparently, the elasticity of the polyurethane adhesives is higher than with traditional hot melt adhesives. The accumulation of fibers on the nozzle is particularly undesirable because one fiber extending across the air flow tends to cause other fibers to accumulate on the nozzle thereby deteriorating and sometimes destroying the spray pattern altogether, thus rendering the nozzle inoperable.
Accordingly, it is an objective of the present invention to provide a nozzle assembly which produces a stable spray pattern when used with polyurethane adhesives and which consistently retains its defined shape and dimensions.
It is a further objective of the invention to produce a spray pattern that is sufficiently wide to be practical for use in various applications, and particularly automotive applications.
It is a further objective of the present invention to provide a nozzle which prevents fibers or strands of adhesive material from contacting and sticking to the nozzle assembly and thereby prevents shifting or complete destruction of the spray pattern.